Posts by Edward Perez64

Overview the 520 ERROR

Think of the 520 error as a bit of a "catch-all." It basically happens when the origin server sends back something weird—something the system just doesn't know how to deal with, like a protocol violation or a totally empty response.

While you can run into some pretty bizarre edge cases, most of the time it boils down to a few common culprits:

Connections getting reset right after a successful TCP handshake
Headers hitting the Akamai limit (anything over 8kb)
The origin server sending nothing back
An invalid HTTP response
An HTTP response that's missing its headers entirely

If you can pin down one of these issues on your actual webserver, your best bet is to reach out to your hosting provider. They can help tweak the server config so things stop breaking.

Common Causes 520

These errors usually live at Layer 7—the Application Layer. In plain English, that means the app itself is spitting out a bad response. Sometimes, things like rate limiting or aggressive request filtering (like blocking certain IPs or high-volume traffic) can trip this up.

Troubleshooting due to the nature of the 520 response

Since the 520 is such a vague error, I'd suggest testing the origin server directly. Using a cURL command is a solid way to see if the server is actually sending back an empty reply, a messed-up HTTP response, or headers that are just way too massive.

Here’s a quick example of how to force the Host HTTP header when hitting the source IP where the domain lives (I'm using a login page for this example):

curl -vso /dev/null --user-agent "Mozilla 5.0" -H "Host: example.com" http://123.123.123.321/login

Check out this example output where the origin gives an empty reply. If this were being proxied by Akamai, it'd trigger that 520 error immediately:

* Hostname was NOT found in DNS cache
* Trying 123.123.123.321...
* Connected to 123.123.123.321 (123.123.123.321) port 80 (#0)
> GET /login HTTP/1.1
> User-Agent: Mozilla 5.0
> Accept: */*
> Host: example.com
>
* Empty reply from server
* Connection #0 to host 123.123.123.321 left intact

On the flip side, a healthy header should look more like this:

* Hostname was NOT found in DNS cache
* Trying 123.123.123.321...
* Connected to 123.123.123.321 (123.123.123.321) port 80 (#0)
> GET /login HTTP/1.1
> User-Agent: Mozilla 5.0
> Accept: */*
> Host: example.com
>
< HTTP/1.1 200 OK
< Content-Type: text/html
< Date: Day, DD, Month Year Hour:Minute:Second Timezone
{ [14240 bytes data]
* Connection #0 to host 123.123.123.321 left intact

Since rate limiting can be a factor, make sure you've whitelisted our IP ranges. You can grab the full list here.

Another move is to grab an HAR (HTTP Archive File) from a user who's actually seeing the error. Comparing a request made directly to the origin versus one going through the proxy is super helpful for seeing if those headers are getting too bloated.

If you end up opening a support ticket, try to include:

The exact steps to recreate the error
Any HAR files you've collected
The Request IDs from the errors you're seeing

So, this is what’s popping up on that subforum:

Error 520 Request ID: 2a23d533382c1a24 • 2016-05-13 05:50:25 UTC
Web server is returning an unknown error

What happened?

There is an unknown connection issue between Akamai and the origin web server. As a result, the web page can not be displayed.

What can I do?
If you are a visitor of this website:

Please try again in a few minutes.
If you are the owner of this website:

There is an issue between Cloudflare's cache and your origin web server. Cloudflare monitors for these errors and automatically investigates the cause. To help support the investigation, you can pull the corresponding error log from your web server and submit it our support team. Please include the Request ID (which is at the bottom of this error page). Additional troubleshooting resources.

Cloudflare Request ID: 2a23d8c4cc083964 • Your IP: xxx.xxx.xx.xxx • Performance & security by Cloudflare

Posting works perfectly fine over here, but on that other thread, I keep getting hit with that error I mentioned earlier!

I’ve been getting this "server offline" error for basically 24 hours now, and it’s totally blocking me from posting anything. I can still scroll through and read threads, but that’s just because everything is pulling from my cache. Anyone actually know what’s going on?

Hey mods, still waiting on an answer about where my post went. I’ve got info for the next part that basically tears down everything Goldstein is saying regarding those post-war execution lists—not just limited to places like Auschwitz, but happening all over the former territory.

And honestly, how are we supposed to react when you see a guy in a photo straight up admitting he wasn't a "participant" per se, but was just "doing his job"?

Why is this being shut down here? Isn't this exactly the kind of heavy-hitting stuff that belongs on PDF Poitik?

I just started a new thread over on PDF Poitik with this title.

It didn't take long before I got a notification saying it was moved!

Since the search function is being a total pain right now, could the mod who moved it just let me know where it ended up?

Also, I'd love to know what was actually wrong with it—what made it "not directly related" to PDF Poitik?